Water-soluble yarn



United States Patent WATER-SOLUBLE YARN Theodore Rudolph Latour, Sharptown, Md., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 1, 1951, Serial No. 254,434

5 Claims. (Cl. 18-54) This invention relates to a process for producing watersoluble polyvinyl alcohol yarn of improved properties.

The demand for a water-soluble yarn has been increasing steadily for several years. Uses for such yarn include various plied structures wherein the water-soluble yarn is used as a strengthener for very fine yarns during weaving or other fabrication steps. They may be plied with cotton, nylon, or other synthetic polymer yarn and subsequently dissolved from the fabric.

A preferred polyvinyl alcohol material for this use is grade 52-22 Elvanol manufactured by E. I. du Pont de Nemours and Company, inasmuch as this polymer type exhibits complete and rapid solubility in hot and cold water. It is about 88% hydrolyzed polyvinyl acetate. Polyvinyl alcohols which have been hydrolzed to substantially higher or lower degrees are not as suitable for the manufacture of water-soluble yarns since they are not as readily water-soluble.

The very fact that the most satisfactory material is rapidly and completely soluble makes it diflicult to prepare products with filament properties necessary to withstand the required textile operations and storage under normal humidity conditions while yet retaining the needed ease of solubility.

It is of course known that water-soluble polyvinyl alcohol yarns coagulated in highly concentrated salt solution can be rendered more diflicultly soluble in water by aftertreatment as, for instance, with boric acid which may affect a partial cross-linking and blocking or substitution of the water-sensitive hydroxyl groups. However, this is undesirable for the purpose of this invention for, while the salts of coagulation must be removed without re'dissolving the yarn, the yarn must remain in a readily soluble form while maintaining desirably high tenacity, elongation and modulus of elasticity within the filaments.

It is, therefore, an object of this invention to provide a process for producing stabilized water-soluble yarn of improved properties for the above-mentioned textile purposes. Other objects will become apparent from the description and the appended claims.

This invention comprises spinning a solution of 82% to 94% saponified polyvinyl ester into a concentrated sulfate salt coagulating bath, removing such sulfate salt from the resulting yarn with an aqueous solution of a volatile salt containing a small concentration of boric acid, and drying the yarn at elevated temperature to remove the volatile salt as well as the water.

Preferably the saponified polyvinyl ester is grade 52-22 Elvanol, an 88% saponified polyvinyl acetate, but any other saponified polyvinyl esters may be used, e. g., polyvinyl formate, polyvinyl propionate and polyvinyl butyrate, and the degree of saponification may be varied from about 82% to 94% depending on the polyvinyl ester and the viscosity of the polymer.

The sulfate salt coagulating bath may be the usual type, i. e., sodium sulfate, ammonium sulfate or mixtures thereof. Preferably the bath consists of about 45% am- 2,716,049 Patented Aug. 23, 1955 monium sulfate, although the concentration may vary from 40% to saturation.

The aqueous solution of a volatile salt may be a concentrated solution, e. g., 40% to 60%, of ammonium acetate, ammonium formate, ammonium oxalate, ammonium carbonate, ammonium bicarbonate, or other salt which is volatile below temperatures which would injure the yarn. In this aqueous, volatile salt bath about 1% of boric acid is dissolved. This boric acid concentration may be varied from 0.5% to as much as 2% without adverse eifect but 1% appears to be about optimum.

Best results are obtained under certain conditions of spinning, lagging before drawing, drawing 4 to 8 times, washing and drying, as will be shown by the examples that follow.

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EXAMPLE 1 A yarn of sixty filaments was spun from a 20% aqueous solution of about 88% saponified polyvinyl acetate (type 52-22 Elvanol) by extruding the solution 'into a 45% ammonium sulfate bath at 70 C., leading the yarn through the bath a distance of about 13 inches to a drawofi wheel at 25 yards per minute and, after several passes around the wheel, to a bobbin rotating at the same peripheral speed as the draw-off wheel, on which bobbin the yarn is wound up. This yarn of about 1300 denier, calculated on the basis of the polymer present, was held sev eral hours and then drawn through a 30% ammonium sulfate bath at 60 C. to a second bobbin at a draw ratio of 4.6X. From this bobbin, yarn was withdrawn and passed through 60% ammonium acetate bath at 25 C., to replace substantially all the ammonium sulfate with ammonium acetate, and the yarn was again wound on a bobbin. After centrifuging, the bobbin of yarn was subjected to overnight drying at 35 C. and, thereafter, to overnight drying at C. This is sample A in the table below. Another sample of yarn was similarly prepared except that the ammonium acetate washing bath also contained 1% boric acid. This is sample B in the table below.

Table I Yield Point Tenacity, Sample Denier Modulus gmJ 3 3 5,;

Tensile Elong. dame! It will be noted that the sample treated with boric acid showed a marked improvement in modulus and yield point and noticeably higher tenacity. When these two samples were subjected to solubility tests under low tension (i. e., 0.02 to 0.1 gram per denier) sample A was found to break in about thirty seconds in water at 1 C., while sample B required a water temperature of about 37 C. to bring about tensile failure in the same time. This decrease in solubility points to some chemical reaction having taken place between the polyvinyl alcohol and boric acid, but the surprising part is that this modified product is still relatively soluble and entirely satisfactory for commercial use, while acquiring much needed stability for textile processing and storing. The following data are given to bring out further advantages gained from the use of this invention.

Comparative data on tensile recovery, wherein samples were subjected to stress to elongate them 1% and 3%, as indicated, and then allowed to recover, show desirable tensile recovery properties resulting from this boric acid treatment. Sample B was compared with a sample designated C in the tabulation below and prepared as described above for sample A and with properties very much like sample A.

G; The following results were obtained from tests on these samples Table IV Denier Yield Point A A Tensile Recovery Elong.,

53a percent Modulus Tensile Elong. 1%

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Table ll 7 Tenacity, Elong. Tensile Recovery Denier Modulus percent Sample denier 7 Table III Shrinkage at 60% Relative Humidity, percent Sample 1 day 3 days This reduction of shrinkage gained by the use. of boric acid is'desirable in order that the polyvinyl alcohol component of a plied yarn shall not shrink and cause unsightly 'puckering, or the like, during use before it is washed out. Moreover, it minimizes tightening of the yarn on the package during storage.

7 EXAMPLE 2 I Thespinning, lagging, drawing and washing steps were carried out in much the same manner as described under 7 Example 1. In this case, however, the coagulating bath was composed of 47% ammonium sulfate maintained at a temperature of C. The draw bath was 50% ammonium sulfate at C., and the draw raito was 63X. Again, the ammonium sulfate was displaced by passing it through a 60% ammonium acetate bath at 25 C. for the Starting with less readily soluble polyvinyl alcohol, wet spun yarns could not be directly produced or modified to give as desirable physical properties with satisfactory solubility whereas, by the use of this invention, polyvinyl alcohol yarns of excellent textile properties may be pro- 7 duced. These yarns caneasily be plied with yarns of cotton,,rayon, nylon, polyesters, polyacrylics and of other synthetic filament-forming polymers to produce improved and useful composite'yarns, the polyvinyl alcohol yarn component being easily removed by washing in luke-warm water, i. e., from to 110 F.

Since many difierent embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.-

What is claimed is: t

i 1. A process for stabilizing freshly spun yarn formed by spinning a solution of 82% to 94% saponified polyvinyl ester through a spinneret into a concentrated sulfate salt coagulating bathvwhich comprises removing the sulfate salt from the yarn with a concentrated aqueous solution of a volatile salt containing from 0.5% to 2.0% of boric 'acid and drying the yarn at elevated temperature to remove the water and volatile salt. 2. A process as definedin claim 1 in which the saponi- V fied polyvinylester is saponified polyvinyl acetate.

control sample designated F, while 1% boric acid was added to the ammonium acetate displacement bath for the. production of the yarn of this invention designated sample 3. A process as defined in claim 1 in which the saponified polyvinyl ester is 88% saponified polyvinyl acetate.

4. A processas defined in claim 1 in which the volatile salt is an ammonium salt and the concentration of the volatile salt solution is from 40% to 60%.

5. A process as defined in claim 1 in which the concentration of. boric acid in the volatile salt solution is about 1%. 2

References Cited in the file of this patent v "UNITED STATES PATENTS 2,236,061 Izard et al. Mar. 25, 1941 2,388,325 Houtz Nov. 6, 1945 2,591,242 Drisch et al Apr. 1, 1952 FOREIGN PATENTS 343,168 Japan April 27, 1943 

1. A PROCESS FOR STABILIZING FRESHLY SPUN YARN FORMED BY SPINNING A SOLUTION OF 82% TO 94% SAPONIFIED POLYVINYL ESTER THROUGH A SPINNERET INTO A CONCENTRATED SULFATE SALT COAGULATION BATH WHICH COMPRISES REMOVING THE SULFATE SALT FROM THE YARN WITH A CONCENTRATED AQUEOUS SOLUTION OF A VOLATILE SALT CONTAINING FROM 0.5% TO 2.0% OF BORIC ACID AND DRYING THE YARN AT ELEVATED TEMPERATURE TO REMOVE THE WATER AND VOLATILE SALT. 